The present invention relates to a method for disposing an inner insert or inserts in blow molding and more particularly a method for mounting a molded insert or inserts on the inner wall of a product when the latter is being shaped by blow molding.
In disposing inserts onto a product which is being shaped by blow molding, the molded inserts of material capable of being welded to a plastic parison are pressed against the parison under the pressure of 2-10 kg/cm.sup.2 until the molded inserts and parison are cooled to solidify. In the case of an outer insert to be disposed on the outer wall surface of a parison in blow molding, the insert is disposed in position on the cavity of a mold so that the parison is caused to be pressed against the outer insert under a blowing pressure, whereby the outer insert is easily disposed in position. However, as to an inner insert to be placed within a parison, no effective means has been proposed for holding a device adapted to press the inner insert to a parison. Even when an inner insert is attached to the inner wall surface of a parison by virtue of an adhesive tape, it is impossible to keep the inner insert in position during blow molding since no force is available for keeping the inner insert in position. Thus, hitherto, it is impossible to dispose an inner insert or inserts in position within the parison.
A conventional countermeasure in this respect is as follows. In blow molding of for instance a gasoline tank made of plastic material and in which a reservoir or chamber for gasoline is defined, the tank main body is blow-molded and then is removed from a mold. An opening greater than 150 mm in diameter is formed through the upper wall of the molded main body and a reservoir or chamber is placed through this opening into the main body. Such process requires a further step for securely disposing the reservoir in the main body by an ultrasonic welding technique. Moreover, the opening thus formed and large in diameter is difficult to seal and will cause the reduction in strength of the gasoline tank.
In view of the above, the present invention has for its object to provide a method for disposing an inner insert or inserts in blow molding which permits the welding or attachment of the inner insert to a main body during blow molding so that the quality of a molded product can be considerably improved and further fabrication steps required after the blow molding step can be substantially eliminated, whereby costs of molded products can be decreased. No separate storage of inner inserts is needed during blow molding so that not only a space for storage but also a working space can be remarkably reduced.